This invention relates to wheelchairs. Specifically, it has application to wheelchairs that can be employed to provide mobility for a person who is unable, or who has limited ability, to walk.
The most common design of wheelchair is propelled by a user using his or her hands to apply a turning force to rings secured to each of two main wheels of the wheelchair. However, it is well-recognised that this arrangement is not without its disadvantages. Conventional wheelchairs convert a user""s efforts into motion with relatively low mechanical efficiency, not least because a user can apply force to the wheel in relatively short and discrete pulses. After time, a user""s hands may be damaged by the efforts they are required to make. The action that a user must perform is not easy, particularly for those people who have limited use of their hands. Moreover, it is not pleasant for a user to have to directly handle wheels that are in such close contact with what is often a dirty environment. These disadvantages encourage users to adopt wheelchairs that are electrically propelled. However, this deprives the user of physical exercise, which they may be unable to obtain in other ways, and is not available to all people due to expense.
An aim of this invention is to provide a wheelchair and a drive system for a wheelchair that is more efficient and more amenable to its user.
From a first aspect, this invention provides a wheelchair comprising a drive system that includes an input member carried for oscillatory movement on a frame of the wheelchair, and a transmission system disposed to mechanically interconnect the input member to a ground-engaging wheel carried for rotation on the frame, the transmission system being configured such that oscillatory movement of the input member causes rotational movement of the wheel, thereby enabling a user of the wheelchair to propel it by applying effort to the input member.
It has been found that the required oscillatory movement can readily be applied by a user to the input member to cause drive to be applied to the wheel over a comparatively large proportion of its rotation. This can be achieved by a user making contact with the input member and without requiring the user to make direct contact with the wheel (or any component directly attached to the wheel).
A typical wheelchair embodying the invention includes two (or more) ground-engaging wheels. In such embodiments, there is typically provided a respective transmission system for each of the wheels. Preferably, each transmission system is connected to a respective input member, the input members being configured such that they may be moved by a user independently, or at least partially independently, of each other, whereby a user can selectively cause one or other of the wheels to be driven. In this way, the user can effect steering control.
The input member is most typically mounted for oscillatory movement along a linear path. For example, it may be a substantially rectilinear path. The path may be in a direction that has a substantial component in a direction of normal forward motion of the wheelchair. In such a configuration, the user operates the input members with a fore-and-aft pushing movement. In embodiments that include two input members, they may be disposed for motion along paths that are approximately symmetrical about a central axis of the wheelchair.
The transmission system may include a first drive gear that is caused to be driven by movement of the input member. For example, the input member may be connected to the first drive gear by a flexible connecting element such as a chain or a cable. The first gear may be in mesh with a wheel gear. Drive may be transmitted to the wheel by a wheel gear, in which case the wheel gear and the wheel are typically secured for rotation together in a first direction. The wheel gear and the ground-engaging wheel may be free to rotate with respect to one another in a second direction, such that the wheelchair can freewheel in a forward direction. For example, the wheel gear and the wheel may be interconnected through an overrunning clutch.
In an advantageously compact arrangement, the transmission system is incorporated into a hub unit of a ground-engaging wheel.
The extent to which the ground-engaging wheel turns upon each movement of the input member (referred to as the xe2x80x9cdrive ratioxe2x80x9d in this specification) can be determined by relative sizes of components of the transmission system. The drive ratio is selected so as to avoid the need for the user to move the input member excessively rapidly in order to make satisfactory progress. At the same time, the drive ratio must be such as to ensure that the user need not apply excessive force in order to move the wheelchair. Advantageously, the transmission system is configured such that the drive ratio can be selected in order to meet the requirements of a specific user. The transmission system may furthermore be configured such that the drive ratio can be varied by the user while the wheelchair is in use.
A wheelchair embodying the invention most advantageously further comprises a braking system. The braking system may be incorporated into a housing in common with the transmission system.
Advantageously, the drive system may be readily applied and removed from a wheelchair. In such embodiments, the wheelchair may be propelled in a conventional manner when the drive system is not applied to the wheelchair.